Two-part winding mandrel



July 8', 1969- P. w. MAFTlNCIC I 3,454,237

TWO-PART WINDING MANDREL Filed Aug. 28, 1-967 Sheet of 3 J 8, 1969 P. w. MARTINCIC 3,454,237

-PART NDRE Filed Aug. 28. 1967' Sheet 2 of3 Sheet 3 of :5

July 8, 1969 P. w. .MARTINCIC TWO-PART WINDING MANDREL Filed Aug. 28. 1967 FIG.7.

FIGJZ.

FIG.|I.

M d in Q. M J v m w 2 F w m PM r b IL 6 Huh 4. 4

United States Patent US. Cl. 24272.1 4 Claims ABSTRACT OF THE DISCLOSURE A two-part winding mandrel for winding electrical coils from sheet conductors. The mandrel comprises two identical separable parts having means for forcing the two identical parts apart and also means for limiting the distance the two parts may be forced apart by a predetermined distance. The two identical parts of the mandrel are molded from polyether-urethane foam in a metal mold. The two identical parts of the mandrel have a high density and high resistance to deterioration when thermocycled. The two identical parts of the mandrel may be separated a predetermined distance for winding a coil thereon and then moved toward each other by removing the means for forcing them apart to facilitate removing the coil from the mandrel after it has been wound.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a two-part expandable mandrel for winding electrical coils from sheet conductors and more particularly to an expandable mandrel made from polyether-urethane foam, or other suitable resins, winding electrical coils for transformers, reactors and other electrical apparatus.

Description of prior art To manufacture the type of coil made on the mandrel provided by this invention, the coil is wound from a sheet conductor under tension, such conductor being aluminum or copper or the like. The aluminum or copper sheet conductor has enameled insulation thereon with a B-stage, or partially cured resin overlay, such as epoxy, over the enameled insulation. After the coil has been wound it is heated while still on the mandrel by passing alternating current through the winding to post cure or set the resin overlay to stick all of the turns of the coil firmly together, or to fix the coils. Wooden mandrels, such as dense maple, have been used to wind such coils in the past; however, these dense maple mandrels were not satisfactory since the high temperature to which the turns of the coil must be heated to cure the resin overlay on the sheet conductor charred the wood. This charring made it ditlicult to remove the coil from the mandrel and it also caused parts of the mandrel to warp or chip away and that changed the dimension of the mandrel and destroyed its usefulness as a winding mandrel. Metal mandrels have also been tried, but found to have serious disadvantages. Any metal mandrel is a good heat conductor and it was found that the metal mandrel conducted heat away from the coil turns so fast during the process of curing the resin overlay on the coil turns that it took a very long time with high current and became expensive to cure the resin overlay on the coil turns while the coil was still on the mandrel. It was also found that with metal mandrels a large portion of the electrical energy supplied to the windings to cure the resin overlay on the conductor was consumed in induction heating of the mandrel, rather than to cure the resin overlay on the winding. Metal mandrels are also subject to exces- "ice sive expansion and changing of dimensions when thermocycled during the curing of the resin overlay on the sheet windings.

SUMMARY OF THE INVENTION This invention provides a two-part expandable mandrel made from high density polyether-urethane foams, or other suitable resins. The mandrel is of such density that the coil conductor having a resin overlay thereon may be wound on the mandrel under tension. The coils and the mandrel may be repeatedly heated by passing alternating electrical current through the turns of the coil to cure or set the B-stage resin overlay on the sheet conductors without any deleterious affect to the mandrel. The mandrels may be repeatedly thermocycled during the curing of the resin overlay and they do not warp, chip or otherwise change dimensions as is the case with Wooden or metal mandrels.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a partial perspective view, with parts broken away for clarity, illustrating a mold for making one part of one embodiment of the mandrel provided by this invention;

FIG. 2 is an exploded view of one embodiment of the mandrel provided by this invention;

FIG. 3 is a top view of one of the expander elements used in the mandrel of FIG. 2;

FIG. 4 is a side view of the expander element illustrated in FIG. 3;

FIG. 5 is a perspective view showing the mandrel of FIG. 2 mounted on a winding machine, with a coil being Wound on the mandrel;

FIG. 6 is a perspective view showing another embodiment of the mandrel provided by this invention, mounted on a winding machine with a coil being wound on the mandrel;

FIG. 7 is an end view of one of the molded parts of the mandrel shown in FIG. 2;

FIG. 8 is a view of the part shown in FIG. 7 looking in the direction of the arrows V'IIIVIH;

FIG. 9 is a side view of the part shown in FIG. 7;

FIG. 10 is a plan view of one of the molded parts of the mandrel shown in FIG. 6;

FIG. 11 is a view of the parts shown in FIG. 10 looking inthe direction of the arrows XIX'I;

FIG. 12 is a side view of two of the molded parts of FIG. 10 assembled for winding a coil as shown in FIG. 4;

FIG. 13 is a longitudinal sectional view and FIG. 14 is an end vie-w of an expander plug used in the mandrel of FIG. 12;

FIG. 15 illustrates a molded metallic duct former held in position by one of the restraining clamps shown in FIG. 2; and

FIG. 16 illustrates two electrical coils after being removed from their respective winding mandrels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the description like reference characters refer to like parts on the various figures of the drawings.

Referring specifically to the drawings, FIG. 1 illustrates a mold 10 of the type which is used for making the molded parts of the mandrel provided by this invention. The mold 10 is made of metal and it may be assembled by welding the parts together with a removable top and bottom for extracting the molded part or it may be any other construction that is known in the art. The interior of the mold is shaped to provide the exterior shape to the part formed in the mold. The interior of the mold is lined with a material such as polytetrafiuoroethylene as illustrated at 12 This liner 12 sticks to the molded part and is removed from the mold when the molded part is removed. The purpose of this liner 12 will be explained more thoroughly hereinafter. A vent hole 14 is illustrated at the top of the mold to permit air to escape and to permit pressure release on the inside of the mold during the molding process.

The molded part is formed by filling the mold with a foaming resin such as polyether urethane or any other of the foamable resins such as phenolics, epoxies, silicones, Styrofoam and the like. The process described in detail in US. Patent No. 3,072,582 may be used for molding the parts, with modification of temperature and curing time as pointed out hereinafter.

The molding agents and resins used in this molding process may be any of those described in the US. Patent No. 3.072.582.

The two main parts of the mandrel are identical and they are both molded in the same mold illustrated by the reference character 10.

FIG. 2 is an exploded view of a two part expandable mandrel as provided by this invention. The two identical molded parts of the mandrel of FIG. 2 are illustrated by the reference characters 16 and 18. The two parts 16 and 18 are identical in shape and are molded by foaming resin in a mold such as illustrated in FIG. 1. It is seen from FIG. 2 that each of the parts 16 and 18 has onehalf of an opening 20 therein. The opening 20 is shaped like a double frustum of a cone with the smallest diameter 22 near the center of the opening.

Each of the parts 16 and 18 also have identical slots 24 in each end thereof. To assemble the mandrel for winding an electrical coil thereon from a sheet conductor the two identical parts of the mandrel 16 and 18 are placed together so that the two halves of the opening 20 in each of the parts 16 and 18 match and provide a double frusto-conical opening through the center of the mandrel. A pair of channel or bracket members 26 are provided, each of which has a web portion 28 and a pair of perpendicular side portions 30 extending from the web portion 28. The channel or bracket members 26 also have extending therefrom in a direction opposite from the side portions 30 a pair of angular brackets 32 and 34. The purposes of the brackets 32 and 34 will be explained hereinafter.

After the two parts 16 and 18 of the mandrel have been placed together so that the two halves of the openings 20 in the parts 16 and 18 match, the extending side portions 30 of the channel members 26 are placed in the grooves or slots 24 at each end of the molded parts 16 and 18. To hold the two parts of the mandrel 16 and 18 and the channel members 26 in an assembled relationship a conical plug 36 is placed in the conical opening 20 from each side of the mandrel. The two conical plugs 36 have the same general configuration as the openings 20 in the two parts 16 and 18 of the mandrel. The conical plugs 36 have two holes 38 therethrough. Bolts 40 are placed through the holes 38 in both of the plugs 36 and nuts 42 placed thereon and tightened to draw the two plugs 36 toward each other. Due to the frusto-conical configuration of the opening 20 in the two parts 16, 18 of the mandrel, as the two frusto-conical plugs 36 are drawn toward each other the two parts 16 and 18 of the mandrel are moved away from each other until the extending side portions 30 of the channel member 26 are drawn tightly against the surfaces 44 of the slots 24. This tightly binds the two parts 16 and 18 of the mandrel together so that the mandrel may be handled or mounted on a winding machine without becoming disassembled. The mandrel is held in this position with the two parts 16 and 18 separated by a predetermined amount, which amount is determined by the width of the slots 24 in the ends of the foam molded parts 16 and 18. The distance by which the two parts 16 and 18 of the mandrel are separated during winding of the coil thereon from sheet conductor is approximately 4 inch. This distance is provided by 4 the width of the slots 24 in the ends of the parts 16 and 18.

FIG. 3 shows a top detail of one of the separating plugs 36 and FIG. 4 is a side view of the plug illustrated in FIG. 3 to show the tapered sides of the plug 36 and the openings 38 and 52 therethrough.

FIG. 7 is an end view of one of the molded parts 16 and 18 as shown in FIG. 2. The mandrel comprises two of these identical parts. FIG. 8 is a top view of the part shown in FIG. 7 looking in the direction of the arrows VIIVII of FIG. 7 to illustrate the double frusto-conical half opening through one of the parts 16 and 18. FIG. 9 is a side view of one of the molded parts as shown in FIG. 7 and further illustrates the shape of the doubled frusto-conical opening through the part and also illustrates how the slots 24 extend the entire length of the molded parts 16 and 18.

FIG. 15 illustrates the purpose of the bracket members 32 and 34 extending rearwardly from the web 28 of the channel 26. The reference character 46 illustrates an eX- truded metal duct former which is placed on the mandrel before a coil is wound thereon from sheet conductor. In order to hold this duct former 46 in place on the mandrel before the coil is wound thereon the duct former 46 is provided with a keyway or a slot 48 which fits over the brackets 32 and 34 on the channel member 26. The brackets 32 and 34 hold the duct former 46 in place until the coil is wound on the mandrel; however, after the coil has been wound and the mandrel is disassembled the channel member 26 may be removed and the duct former 46 left in place in the coil.

It has been found that mandrel parts 16 and 18 foam molded from resins with a density of from 15 to 60 pounds per cubic foot are satisfactory. It has been found that the foamed resin having a density of approximately 30 pounds per cubic foot is particularly satisfactory. It is necessary that the foam molded parts 16 and 18 be of relatively high density because the sheet conductor is wound on the mandrel under tension which would cause a material of low density to crack or compress or change dimensions.

It has been found that to obtain satisfactory molded parts 16 and 18 that before molding the parts the metal mold 10 should be heated to a temperature of approximately F. to P. Then the prepared resin is poured into the mold at a temperature of 160 and permitted to cure or foam for 20 minutes. The parts 16 and 18 are then removed from the mold 10 and postcured at 350 F. for two hours. It has been found from experience that close adherence to this process is important to obtain the best results for the molded parts 16 and 18.

After the mandrel of FIG. 2 has been assembled as described hereinbefore it is then placed on a spindle 50 of the winding machine by inserting the spindle 50 through holes 52 in the tapered plugs 36. The mandrel is held on the winding machine by a nut 54 which is threaded onto the spindle 50 of the winding machine. FIG. 5 illustrates the mandrel for winding a high voltage coil for a transformer from sheet aluminum or copper 56. The sheet aluminum or copper 56 is fed ofi' a storage reel (not shown). The sheet aluminum or copper 56 has an enamel coating thereon with a B-stage, or partially cured, resin overlay coating over the enamel coating. After the coil has been completely wound the mandrel is removed from the spindle 50 of the winding machine and an alternating current is passed through the winding 56 to heat the winding to a temperature sufficient to cause the resin overlay on the sheet conductor 56 to soften and completely stick all of the turns of the coil together. It was found with the use of wooden mandrels such as hard maple that this temperature to which the resin overlay must be heated to cause the turns of the coil to stick together was sufficiently high to cause the wooden materials to char and crack and change their dimensions upon repeated use. This was very unsatisfactory since the wooden mandrels were expensive to make. It was also found with metal mandrels, that the metal being a good conductor thermally conducted heat away from the windings and substantially extended the time to which the windings had to have current pass therethrough in order to set or cure the resin overlay on the sheet 56. It was also found that the metal mandrels conducted heat away from the windings 56 because the metal mandrels were also heated by induction. All of these things increases the length of time required to cure the resin overlay on the windings 56 and requires more electrical energy than the mandrel provided by this invention.

After the required number of turns of the coil have been wound on the mandrel as illustrated in FIG. 5 and the coil has been set by passing alternating current through the turns until the resin overlay on the conductor 26 has firmly cemented all of the turns together the bolts 40 are released and the expander plugs 36 are removed from the mandrel. The two parts 16 and 18 of the mandrel may be moved toward each other a suflicient distance so that the two identical parts 16 and 18 may be easily lifted out out of the coil by moving them upwardly. The channel members 26 are then removed from the duct former key- Way 48 leaving the duct former 46 cemented to the coil assembly by the resin overlay on the sheet 56.

As explained hereinbefore the outside of the molded parts 16 and 18 are covered with polytetrafluorine, commercially known as Teflon, this material is of such character that the resin overlay on the conductor sheet 56 will not adhere thereto. After the tapered expander plugs 36 have been removed from the mandrel, the two parts 16 and 18 of the mandrel may be moved toward each other and then lifted out of the coil. The reference character 58, FIG. 16, illustrates a high voltage coil for an electrical transformer after it has been removed from the winding mandrel. The coil 58 comprises a plurality of turns of sheet conductor firmly cemented together by the resin overlay on the sheet conductor 56.

FIG. 6 illustrates a second embodiment of a foam molded mandrel for winding a low voltage coil of an electrical transformer. The mandrel of FIG. 6 comprises two main molded parts 60 and 62 which are identical and which may be foam molded in the identical manner as has been described hereinbefore for the parts 16 and 18 of the mandrel of FIG. 2. It is also emphasized that the area of the parts 60 and 62 which are contacted by the sheet conductor 80 are also covered with polytetrafluoroethylene, commercially known as Teflon, to prevent the resin overlay on the sheet conductor 80 from sticking to the mandrel parts 60 and 62 during the winding and curing operation. FIG. illustrates a detail of one of the parts 60 and 62, which are identical. The mandrel is composed of the two identical parts 60 and 62 and the two parts 60 and 62 when placed together for winding a coil thereon from sheet conductor have a pair of tapered openings 64 and 66 therethrough. The openings 64 and 66 are illustrated in detail in FIGS. 10, 11 and 12. The purpose of the tape-red openings 64 and 66 is to permit a pair of tapered hollow plugs '69, such as illustrated in FIGS. 13 and 14 to be inserted into the openings 64 and 66 to hold the two parts 60 and 62 of the mandrel separated. The tapered plugs 69 have straight openings 71 therethrough to permit the mandrel to be mounted on straight spindles 70 and 72 of a winding machine. Nuts 74 and 76 fasten the mandrel on the tapered spindles 70 and 72. As the nuts 74 and 76 are tightened the two parts 60 and 62 of the mandrel tend to separate; however, the extent to which the parts 60 and 62 may separate is limited by bolts 78, located in holes 79, which extend through the two parts 60 and 62. The bolts 78 are illustrated clearly in FIG. 12, which shows the two parts 60 and 62 of the mandrel in assembled relationship as they would be placed on the spindles 70 and 72 of the winding machine. FIG. 11 is a view of FIG. 10 taken along the line XX to illustrate'the positions of the restraining bolts 78.

After the required number of turns of a conductor 80 has been wound on the mandrel, the mandrel is removed from the spindles 70 and 72 of the winding machine and the tapered plugs 69 hold it in assembled position in the coil, and an alternating electric current is passed through the sheet conductor 80 of the winding to heat the resin overlay on the sheet conductor 80 to cause the resin overlay to firmly stick all of the turns of the conductor 80 together. After the winding has been set, or all of the turns have been firmly cemented together by the resin overlay, the tapered plugs 69 are removed from the openings 64 and 66 and the two parts 60 and 62 of the mandrel may be moved toward each other and lifted out of the coil. The coil as it is removed from the mandrel is illustrated by 82 in FIG. 16. As explained hereinbefore, the winding surfaces of the parts 60 and 62 are covered with Teflon, or other suitable release agent 12 to prevent the resin overlay on the sheet conductor 80 from sticking to the mandrel parts 60 and 62.

After the coils 58 and 82 have been removed from their respective mandrels they are nested as illustrated in FIG. 16 and insulated from each other in some suitable manner and provided with a core to provide an electrical transformer.

As set forth hereinbefore foam molded resin having a density of from 15 to 60 pounds per cubic foot has been found satisfactory for providing foam molded mandrel parts for winding electrical coils from sheet conductors. It is essential that the molded parts have substantial density because the sheet windings are wound thereon at relatively high speeds under substantial tension, and substantial density is necessary to prevent the molded part from changing dimensions or cracking or otherwise deforming during the winding operations.

From the foregoing description taken in connection with the drawings it is seen that this invention has provided a new and improved expandable winding mandrel and a method of making the same wherein the main parts of the mandrel are made from a foamed resin which has sufficient density to stand Winding of sheet conductors thereon to provide an electrical coil wherein the conductor may be wound at substantiall high speeds under substantially high tension without deforming the mandrel or without having the mandrel crack or fail. The coils may be set or cemented together while still on the mandrel by passing an alternating coil through the coil to set or cure a B-stage precured resin overlay on the sheet conductor to firmly stick the turns of the conductor together without having the mandrel deform because of thermocycling. 7

I claim as my invention:

1. An expandable mandrel for winding electrical coils comprising two similar parts about which turns of sheet conductor are wound to provide an electrical coil, said two similar parts being made from foamed resin having a density within the range of from 15-60 pounds per cubic foot, first means holding said two similar parts separated by a predetermined distance during winding of the coil, second means limiting the predetermined distance to which said two parts are separated, said two parts being movable toward each other upon release of said means holding said two parts separated to permit removal of the coil from said mandrel.

2. A mandrel as specified in claim 1 wherein said two similar parts are made from polyether-urethane foam.

3. A mandrel as specified in claim 1 wherein said two parts about which the turns of the sheet conductor are wound are covered with polytetrafluoroethylene.

4. An expandable mandrel for winding an electrical coil, said mandrel comprising two parts about which turns of sheet conductor having a resin coating thereon are wound to provide an electrical coil, said two parts being cast from foamed resin having a density within the range of from 15-60 pounds per cubic foot, a release surface on said two foamed resin parts of said mandrel 7 8 preventing said resin on said sheet conductor from sticking to the foamed resin parts of said mandrel, said two FOREIGN PATENTS parts of said mandrel being movable relative to each other to permit removal of said mandrel from inside the 855511 12/1960 Great Bmam' wound coil.

5 NATHAN L. MINTY, Primary Examiner.

References Cited UNITED STATES PATENTS US. Cl. X.R.

2,024,178 12/1935 Morrisey 242-721 29 203 

